Synergistic effects of endophytic bacteria and silicon on controlling common bacterial blight disease in beans

Enhancing the effectiveness of environmentally friendly and sustainable practices in plant disease management is crucial for promoting their wider adoption and use. In this context, the combined use of bacterial biocontrol agents and silicon applications holds significant potential. This study aimed to evaluate the effects of individual and combined applications of endophytic bacteria (EB) and silicon on controlling common leaf blight disease caused by Xanthomonas axonopodis pv. phaseoli (Xap) in beans. Additionally, the effects of these treatments on plant biomass and chlorophyll content were investigated. Bean plants (Phaseolus vulgaris cv. Gina) were grown in a peat/perlite medium under soilless conditions in a climate chamber. Silicon dioxide (SiO₂) (30 mM) and endophytic bacteria were applied to the root collar using the drenching method. The pathogen Xap was inoculated by spraying the leaves, and disease severity was assessed using a 1–5 scale. Plant growth parameters were also recorded. Among the tested EB isolates, Pseudomonas caspiana V30G2 was the most effective in suppressing disease severity. Disease severity was reduced by 31% with V30G2 and by 21% with SiO₂ when applied individually. Notably, the combined application of both agents exhibited a synergistic effect, reducing disease severity by 55%. Although some improvements were observed in specific parameters, such as leaf number, neither the individual nor the combined treatments significantly influenced overall plant biomass or chlorophyll content. Nevertheless, the results suggest that the combined application of silicon and endophytic bacteria, when appropriately selected, has significant potential for environmentally friendly and sustainable disease management, enhancing the disease suppression efficacy of each treatment.